How to automatically generate a last_updated entry in docs

https://gitlab.com/gitlab-com/gitlab-docs/merge_requests/87 introduced a last updated entry at the end of the docs. In order for the last update to show in a document, you need to add the following in the yaml frontmatter:

last_updated: 2017-09-09

Creating a raketask that updates the value automatically based on latest git commit would be great! For ref: https://stackoverflow.com/questions/36948807/edit-yaml-frontmatter-in-markdown-file.

From a bit of a search:

Method 1

Find last updated time:

git log -1 --format=%cd --date=format:'%d %B %Y' $file

which results to a format:

27 April 2017

Method 2

Different method, if we want to use the iso format in yaml frontmatter and output in human readable format:

git log -1 --date=short --format=%cd $file

and then parse with Ruby:

require "time"

ut = DateTime.parse("2017-04-27")
ut.strftime("%-d %B %Y")

@rymai I'd appreciate any help here :)